Calculate your physical, emotional and intellectual cycles, see a 30 or 60 day chart, critical days, a monthly calendar and compare with another person. Entertainment, with no scientific support.
Biorhythm theory proposes that three sine-wave cycles start on the day you are born and repeat forever: a 23-day physical cycle, a 28-day emotional cycle and a 33-day intellectual cycle. Each cycle swings between -100% and +100% by the formula sine(2π x days lived / period), and crosses zero on the so-called critical days. This calculator does that math in your browser, counting whole calendar days (with no time zone or daylight saving error), and lets you pick any reference date, past or future. Beyond the three values for the day, you get a 30 or 60 day chart with the reference day marked and zero crossings highlighted, the list of the next critical days for each cycle, a monthly calendar colored by each day's value, the peak days of each cycle over the next 30 days, a comparison with another person and the option to copy or download the chart as a PNG image. There are also three optional secondary cycles, of 38, 43 and 48 days, found in some popular versions of the theory and treated here as less common extensions. Keep one thing clear: biorhythm has no scientific support. It is a mathematical curiosity, useful as a pattern-spotting game and as a prompt to reflect on your own rhythms, not a prediction.
Every cycle uses the same formula, and only the period changes: value = sine(2π x days lived / period). Days lived is how many whole calendar days have passed between the birth date and the date you are checking. Sine always yields a number between -1 and +1, which we multiply by 100 to get a percentage between -100% and +100%.
Because 23, 28 and 33 have no small common multiple, the three cycles rarely line up, which is why the lines look out of step. A cycle crosses zero every half period: every 11.5 days for physical, 14 for emotional and 16.5 for intellectual. Those crossings are the critical days, and the chart marks them with circles.
The idea began with Wilhelm Fliess, a Berlin physician and friend of Sigmund Freud, who saw 23 and 28 day rhythms in life events and called them male and female cycles. The Viennese psychologist Hermann Swoboda reached similar ideas independently. Later, the teacher Alfred Teltscher added the 33-day intellectual cycle, based on informal observations of student performance.
The theory stayed niche until the 1960s and 1970s, when George Thommen and, above all, Bernard Gittelson (author of "Biorhythm: A Personal Science") turned it into a commercial phenomenon in the United States, with books, pocket calculators and even watches.
The psychologist Terence Hines wrote the most cited review of the literature ("Comprehensive Review of Biorhythm Theory", Psychological Reports, 1998) and concluded that the theory is not valid: well-controlled studies found no relationship between the cycles and performance, accidents or mood beyond what chance explains.
That is why biorhythm is on the list of pseudosciences, alongside many other popular practices. This tool reproduces the classic formula with mathematical precision, but treats the result as entertainment and self-reflection, never as a diagnosis, a prediction or guidance for decisions.
Paste the code into your HTML and the tool shows up on your page, without J-Kit's navigation and ads. It still runs in the browser of whoever visits your site.
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src="https://jkit.tools/embed/en-US/biorhythm-calculator"
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></iframe>These references help contextualize formulas, standards, APIs and limitations used on this page. They do not replace professional validation when a result has legal, financial, medical or operational impact.
It is a popular theory, not a biological measurement, claiming that body, emotions and mind follow fixed sine-wave cycles that start at birth and never change period. This calculator reproduces the classic formula for curiosity and entertainment only.
Enter your birth date to see your cycles.
The dates stay in your browser and are never sent to any server.